This invention relates to indicator systems comprising a container containing an environmental sensing system and cap system separating the sensing system from its surroundings. Indicator systems can be used for the determination of sterilization in a variety of sterilizations processes or in determining the efficacy of an environmental test such as a test for air removal from a sterilization chamber.
In health care, as well as many other industries, it is nearly always necessary to monitor the effectiveness of processes used to sterilize equipment such as medical devices, instruments and other disposable or nondisposable articles, and often waste. In these settings, sterilization is generally defined as the process of completely destroying all viable microorganisms including structures such as viruses, spores, yeasts and fungus. Standard practice in hospitals is to include a sterility indicator in a batch of articles to be sterilized. The use of sterility indicators allows a direct and sensitive approach to assay the lethality of the sterilization process.
A standard type of biological sterility indicator includes a known quantity of test microbial spores. This indicator is placed into the sterilization chamber and exposed to the sterilization process along with the objects to be sterilized. The test microorganisms, for example Bacillus stearothermophilus or B. subtilis spores, are incubated for a specified period of time under conditions which favor proliferation and examined for possible growth, such as turbidity in the growth medium or the presence or absence of certain metabolic products of any surviving microorganisms. Positive growth, indicating the presence of a viable spore, indicates that the sterilization process was insufficient to destroy all of the microorganisms. While the apparatus for containing the spores has varied continuously, the general sterility detection process has not. Many such indicators are disclosed in U.S. Pat. Nos. 3,239,429; 3,440,144; 4,596,773; 4,717,661; 4,732,850 and 5,167,923.
The largest use of sterility indicators occurs in research and the health care industry. Typically, such facilities have limited resources and must reuse their materials and instruments within 24 to 48 hours after sterilization and often immediately. Conventional sterility indicators normally require that the microorganisms be cultured for at least two and often up to seven days to assure adequate detection of any surviving microorganisms. During this time, items which go through the sterilization process, should not be used until the results of the spore viability test have been determined. Consequently, a holding period for sterility verification is often required. This holding period is both impractical and inefficient and, thus, the major drawback of all conventional sterility indicators.
The use of an enzyme and its subsequent activity as an indicator in detecting sterility has been described in U.S. Pat. No. 5,073,488. This technology has been greatly advanced with U.S. Pat. No. 5,486,459 which describes the use of a plurality of interactive enzymes. This technique involves subjecting a set of interactive enzymes to a sterilization cycle. Following completion of the cycle, the set is incubated with a substrate which is acted upon by the enzymes and transformed into a detectable product. Enzyme-modified product can be detected, for example, colorimetrically or fluorometrically. This method has been proven to be accurate and detection speeds are greatly accelerated as compared to spore systems. In fact, definitive results using interactive enzyme technology can be determined in less than a few minutes.
Sterility indicators are often placed in special packaging or wraps to simulate the condition of wrapped goods being processed in a sterilizer. If the articles to be sterilized are in special wrappings or packaging, the sterilant needs to effectively pass through the wrappings to destroy microorganisms on the article. To test the effectiveness of the sterilant passing through additional materials, sterility indicators are placed in challenge packs. These packs impede the sterilant as would the wrappings and thereby represent the conditions of wrapped goods in a sterilizer.
There are international standards such as the International Organization for Standardization (ISO) and the European Standards (EN) that deal with sterilization testing including steam sterilization. International standards dealing with biological indicators and testing procedures are found in the ISO 11138 series and EN 860 series. International standards for the air removal tests for pre-vacuum steam sterilizers comprises a chemical indicator in a test pack are found in the ISO 11140 series and EN 867 series. These packs incorporate the Bowie-Dick test and have similar performance standards as seen in AAMI (American Association of Medical Instrumentation), but use different testing procedures.
AAMI has proposed guidelines for challenge packs containing indicators that are assembled by hospital workers to simulate the conditions of wrapped goods in a steam or ethylene oxide sterilizer. Materials required for an AAMI challenge pack for a steam sterilizer include sixteen freshly laundered huck towels, autoclave tape and sterility indicators. In one method, each towel is folded length-wise into thirds and then folded width-wise in half. Towels are placed one on top of another with the folds opposite each other. Sterility indicators are placed between the eighth and ninth towels and the pack is secured with autoclave tape. The AAMI steam challenge pack is placed into a steam autoclave for the appropriate amount of time. Upon completion of a cycle, the indicators are processed to determine if the sterilization process was sufficient to inactivate the indicators buried in the pack.
In the case of ethylene oxide sterilization, AAMI recommends placing a sterility indicator into a plastic syringe so that the plunger is not touching the indicator. In this case, the needle end of the syringe is open. Two such syringes are placed in the center of a stack of folded towels and the stack is wrapped in a single towel. For routine monitoring, the syringe and indicator can be wrapped in a single towel and placed into a peel pouch.
Tests are also performed that evaluate the effectiveness of air removal in a prevacuum steam sterilizer. Prevacuum steam sterilizers are used to minimize the amount of air present in the sterilization chamber, thus enhancing the penetration of steam into porous loads. A prevacuum sterilizer air removal test is also known as the Bowie-Dick test or a prevacuum sterilizer residual air test.
AAMI guidelines for the Bowie-Dick test pack state that the standard pack is made using folded cotton surgical towels. Several towels are folded to create a stack 10 to 11 inches high with a rectangular border of 9 by 12 inches. A Bowie-Dick test sheet, which comprises a pattern of chemical indicator ink or indicator type on a porous sheet, is placed in the center of the pack. The pack is wrapped in a single cotton wrap and processed in a steam prevacuum sterilizer. The acceptance criterion is that the test sheet or tape darkens uniformly after processing. In other words, the chemical indicator ink changes color upon exposure to steam and if the entire sheet shows a uniform color change, there was no residual air to impede the steam.
AAMI guidelines state that other devices may be used in place of the AAMI challenge packs and Bowie-Dick tests if they provide equivalent results to the AAMI packs. Enclosure of sterilization indicators in various fibrous materials, analogous to textiles such as the towels used in the AAMI challenge packs, has been proposed in U.S. Pat. Nos. 5,200,147; 5,252,484 and 5,223,401. Packages in which a sterilization indicator is surrounded by porous material to replace some of the towels are described in U.S. Pat. No. 4,692,307.
The present invention overcomes the problems and disadvantages associated with current strategies and designs and provides novel methods and test indicators for determining the effectiveness of a sterilization procedure or measuring a parameter of the sterilization process.
One embodiment of the invention is directed to test indicators containing a biological material separated from the sterilizer environment by a cap. In addition, the cap may comprise one or more apertures to control access of the sterilizing medium to the biological material while preventing any biological material from being displaced from the test indicator. In another embodiment, the cap may have a sterilant permeable insert, such as a screen, membrane or mesh, covering one or more apertures in the cap. In yet another embodiment, the cap may have at least one protruding member to prevent mobilization of biological material within a test indicator.
In still another embodiment, the sterility indicator may comprise a modified cap and a compressed, gas-permeable material or a compressed, gas-permeable material without a cap. The compressed material controls access of the sterilizing medium to the biological material within a test indicator. The compressed, gas-permeable material may be formed and inserted into a test indicator as described in Patent Application Ser. No. 09/184,352 and U.S. Pat. No. 5,870,885.
Another embodiment of the invention is directed to a test indicator for determining the effectiveness of a sterilization procedure. Test indicators comprise an outer container having liquid impermeable and substantially gas non-absorptive walls, at least one opening leading into a chamber which contains one or more components of an interactive enzyme system, and a liquid impermeable or liquid semi-permeable gas-transmissive barrier between the components and the opening. These components may be fixed to a solid support or free-floating in a non-aqueous or partially-aqueous solution. After sterilization, the user simply mixes the components in the container with the remaining components of the enzyme system. If any enzyme activity is present, the enzymes plus any necessary coenzymes, cofactors and catalysts will interact with the substrate forming detectable product which can be assayed to determine the effectiveness of the sterilization procedure.
In one embodiment, the remaining components of the enzyme system may be in a separate container and may be transferred from the separate container to a test indicator by a user. In another embodiment of a test indicator comprising a cap with at least one protruding member, the at least one protruding member may contain the remaining components of the enzyme system, including, but not limited to, an indicator solution or growth medium.
Another embodiment of the invention is directed to methods for determining the efficacy of different types of sterilization processes. The test indicator consists of a plurality of interactive enzymes in a container with at least one opening. The opening is either filled with a compressed cylindrical foam insert, or the test indicator is covered with a modified cap, or a combination thereof. The test indicator is placed into the sterilization chamber. The foam insert, modified cap, or both, regulate the amount of sterilant such as steam, gas, chemicals or plasma entering the test indicator to achieve a response that can be equivalent to indicators containing bacterial spores. After the sterilization cycle is complete, the foam insert, if one is present, is removed and the remaining components of the enzyme system are combined. If the proper sterilization conditions were not met, the interactive enzyme system remains active, and a color product forms upon the addition of the remaining components of the enzyme system. If the proper sterilization conditions were met, the sterilant has destroyed components of the interactive enzyme system and no color product is formed. Inactivation of the enzyme system parallels the inactivation of bacterial spores subjected to the sterilization process. Results are available in from a few seconds to a few hours.
Another embodiment of the invention is directed to methods for adjusting the sensitivity of sterility indicators of the invention to one or more predetermined environmental parameters. Test indicators, substantially identical to the sterility indicators, are exposed to a sterilization procedure and the effectiveness of that procedure determined. The position and/or composition of the gas-transmissive plug of another test indicator may be adjusted and the another test indicator is exposed to the sterilization process. From the effectiveness of each test indicator for reacting to the environmental parameter, the sensitivity of the sterility indicator can be accurately and quantitatively adjusted.
Another embodiment of the invention is directed to methods for creating a challenging environment for the penetration of sterilant. Using an enzyme, spore or chemical indicator in a container with a controlled volume of gas-permeable material for creating a reproducible resistance for the sterilant penetration, a test pack for evaluating sterilant penetration or air removal is created.
Other embodiments and advantages of the invention are set forth, in part, in the description which follows and, in part, will be obvious from this description or may be learned from the practice of the invention.